1. Field of the Invention
The present invention relates to a bushing terminal of a vacuum circuit breaker and a fabrication method thereof and, more particularly, to a bushing terminal, a cradle terminal that can be connected to a tulip type contactor constituting a main circuit unit of a vacuum circuit breaker, capable of improving illogical factors of its fabrication process, and a fabrication method thereof.
2. Description of the Related Art
In general, a circuit breaker is classified into a draw-out type circuit breaker and a fixed type circuit breaker. The fixed type circuit breaker is configured to have only a circuit breaker main body which is fixed within a distributing board panel, and the draw-out type circuit breaker includes an outer casing called a cradle facilitating the maintenance of the circuit breaker and allowing only a circuit breaker main body to be drawn in or out.
Here, a draw-out type vacuum circuit breaker is an electronic device that switches a relatively high voltage circuit and interrupts a power supply circuit over a fault current such as a short-circuit current to protect a line (i.e., a cable) and a load device.
With reference to FIG. 1, a main circuit unit of the vacuum circuit breaker includes a bushing terminal 1, a tulip assembly 3, a terminal 4, and an insulating bushing 5. The bushing terminal 1 is inserted into the tulip assembly component mounted at a front end of the main circuit unit of the circuit breaker main body to constitute a conductive line, and there are two types of bushing terminals as shown in FIGS. 2 and 3.
The bushing terminals as shown in FIGS. 2 and 3 include actuator contact portions 1-a and 2-a connected with the tulip assembly 3, booth bar connection portions 1-b and 2-b connected with an external power source and a load side, and flange portions 1-c and 2-c fixed to a cradle or a wall face of a reception casing of the main body. Although the bushing terminal illustrated in FIG. 3 has a different shape as that of the bushing terminal illustrated in FIG. 2, but it has the same function as that of the bushing terminal illustrated in FIG. 2.
The tulip assembly 3 is flexibly fixed to a central shaft of the terminal 4 and movable in a lengthwise direction. When the tulip assembly 3 is insertedly positioned in the bushing terminal 1, it is electrically connected.
The bushing terminals of FIGS. 2 and 3 are the same functionally, and a large air circuit breaker employs the bushing terminal of FIG. 2 while a middle and small air circuit breaker employs the bushing terminal of FIG. 3.
The fabrication methods of the bushing terminals of FIGS. 2 and 3 are different. The bushing terminal of FIG. 2 is fabricated according to a method in which the bushing terminal is divided into two parts and welded, and the flange 1-c is divided in a semi-circular state, inserted into the terminal body and then fixed with a screw or a rivet. Meanwhile, the bushing terminal of FIG. 3 is integrally fabricated by using a casting method, which is then cut so as to be completed.
In this case, the fabrication method of the bushing terminal of FIG. 2 involves various wasteful factors. That is, it takes excessively long working hours, the fabrication unit cost is high because of the necessity of subsidiary materials such as silver, lead, etc, the production costs increases due to a poor productivity, and silver-plating must be performed even on the unnecessary flange portion.
Meanwhile, the fabrication method of the bushing terminal of FIG. 3 has the following problems. That is, because the bushing terminal is fabricated according to a casting method, the period of delivery required for fabrication is lengthened. Also, because its tissue is not densely formed, the conductivity easily deteriorates, and air bubbles included in the bushing terminal may lead to a quality problem. In addition, much time is required for machining after the casting operation, and the flange surface is unnecessarily silver-plated.